When capturing the night time sky, we’re taking a look at factors of sunshine that don’t at all times resolve properly with the lenses we’ve got in our bag. Whether or not the lens is a top-of-the-line “L” from Canon or a third-party lens that value 1/10th the worth, they might each have points with coma and astigmatism. Here is what you are able to do to repair these points and never be caught with an underperforming piece of glass.

If you happen to’ve ever been in any discussion board or possibly a Fb group that facilities round capturing the night time sky and the Milky Manner, you have got in all probability seen somebody asking about a problem known as coma and astigmatism. Each of those points can come up even in lenses which can be the créme de la créme of glass from first-party producers (and are priced accordingly). Coma and astigmatism may seem in third-party lenses that many individuals particularly use for nighttime imaging, however this phenomenon that appears near coma is in actuality a de-centering of the lens parts from incorrect alignment. Many occasions, it’s simpler to return this lens for an additional if it’s nonetheless inside the time-frame to take action. Sadly, not everybody is ready to check their glass earlier than a return window is up they usually could also be caught with a de-centered lens that’s good for daytime capturing, however falls aside when capturing starry night time skies. 

Earlier than we get to fixing the issues, let’s outline every of the problems first. Concerning coma, or comatic aberration, what we’re referring to is an aberration inherent in some lens designs, presumably resulting from imperfection within the lens, or different parts that leads to off-axis level sources, resembling stars, that seem to have distortion just like a tail like a comet. These level sources are likely to appear to be they’re shifting towards the middle of the lens with the “comet tail” pointing within the path of the corners of the picture.

Astigmatism in a lens is the place rays that propagate in two perpendicular planes have completely different foci. If a lens with astigmatism is used to type a picture of a cross, the vertical and horizontal traces can be in sharp focus at two completely different distances. We normally see this concern with a star or any level of sunshine that has wings, and it primarily happens within the corners of the lens because the path towards the middle of the lens is in focus, however a perpendicular line to this focus is out of focus, leading to a “stretched” level of sunshine. That is usually equated to the star having wings.

Astigmatism can happen in even the perfect and priciest lenses as a result of optical design and inherent nature of the lens, which can be primarily based round an ultra-wide aperture. Moreover, this concern may be in lens designs that lack an aspherical ingredient to compensate for the astigmatism that’s inherent within the optical design. Coma tends to be extra of a problem ensuing from poor alignment of lens parts in throughout last meeting and tends to be seen extra typically in third-party lenses of various prices. There will not be any rhyme or purpose as to who receives a duplicate of a lens with coma from a given lens producer if the difficulty is the results of the manufacturing. Extreme coma and astigmatism may be examined beneath any starry sky at a large aperture to substantiate if a lens is exhibiting these points. It’s at all times a good suggestion to check a lens as quickly as attainable after buy to see if coma or astigmatism are obvious in your pictures. If resulting from last meeting, the coma can be constant and will solely have an effect on one nook of the picture, so it’s at all times a good suggestion to shoot a number of pictures in portrait and panorama orientations to substantiate if a nook of the lens is out of alignment. 

So, how can we repair this? Simply check and change our lenses till we discover a good copy? Ought to we take hours in Photoshop making stars that appear to be comets into circles? All of those points exist within the nook of the photographs as a result of the middle of most of those lenses are pristine. Why wouldn’t we simply use the middle of the picture circle the place the celebs appear to be stars? We might have a smaller picture however we are able to at all times take just a few extra pictures, proper?

One of many strategies that I desire and have repeatedly talked up in night time sky imaging is panoramas. It’s simple and requires little or no tools when doing easy panoramic imaging. On this case, we might take three pictures with about 60-percent overlap and have the identical quantity of protection a single picture would have. This additionally means we’re solely going to be stitching collectively the constant a part of the photographs: the middle.

Within the case of say a 14mm lens on a full body digital camera, the place many occasions I’m capturing a thirty-second single publicity, we at the moment are solely including one further minute of labor (two extra pictures) to repair what could also be an inherent optical design concern with possibly a $1,500 lens. For these that could be desirous about noise; sure, we might do stacking right here, however let’s work with one concern at a time. Lightroom and Photoshop each create panoramas seamlessly in publish pretty rapidly with current-generation computer systems and can ignore most points in corners of the body that don’t match the middle, the place the stitching will happen.

Breaking down the best way to shoot this panorama is easy. For capturing a vertical panorama, place your digital camera in panorama orientation and take three pictures with a 60-percent (about 2/3) overlap, elevating your digital camera angle as you seize every picture. If you happen to’re capturing a horizontal panorama, place your lens in portrait orientation and shoot three pictures with a 60 p.c (about 2/3) overlap rotating the digital camera over the ball head. In publish, you mix these pictures in Lightroom or Photoshop and crop to the identical subject of view of the unique lens. You can too crop the coma and astigmatism points out of the panorama, which can be very near the lenses authentic subject of view. Lastly, you can too shoot wider than your single lens can picture and create a nightscape that many have by no means seen earlier than merely as a result of subject of view.

The one further tools for doing easy panoramas could be an L bracket and a nodal slide to appropriate any attainable points with parallax. If you happen to’re capturing panoramas at an ultra-wide subject of view, as an illustration with a 14mm lens on full body, it’s extremely unlikely you’ll ever encounter parallax points with stitching until you’re capturing very shut foregrounds (inside a number of ft of the lens). Additionally, in case you’re solely capturing the night time sky, stars are on the identical aircraft inside our subject of view and consider level and won’t have parallax points. When combining foregrounds and midgrounds into a picture, we usually begin to expertise parallax at lens selections of 24mm and longer (smaller subject of view). When reducing your subject of view, a nodal slide is required for panoramas to keep away from parallax in foreground and midground imaging. Once more, in case you’re capturing with an ultra-wide lens alternative, an L bracket is about all chances are you’ll want and for no different purpose than it’s simpler to rotate a horizontal panorama over the ball head than off to the facet and round a ball head. 

Many panoramas I put collectively are between 24mm and 85mm ,and although it’s attainable to create a panorama with solely an L bracket and a nodal slide, I’d slightly use a panoramic head for medium and telephoto lenses. I personally invested in a 3-axis panoramic head from Nodal Ninja known as the M2 about 5 years in the past (when it was twice as costly) and have used it for almost all my night-imaging for a number of years. When capturing tighter imaging and stitching a panorama from these pictures, you have got an extra good thing about elevated decision measurement of the picture, decreased noise resulting from elevated decision, and the power to create pictures wider than any lens immediately can create in a single seize.

I carry this up as a result of you possibly can go simple or intricate along with your imaging relying on the work you wish to do in publish. Extra pictures means extra work to place every thing collectively on this case. This method makes lenses with the worst coma and astigmatism (ahem Canon’s EF 50mm f/1.2L) close to incredible by merely working across the concern. You might have a plethora of extra choices for lenses this fashion, whether or not it’s a 14mm, 24mm, or a 50mm. Simply bear in mind, the lenses that the majority nightscape and Milky Manner photographers begin out with are on the broader facet, the place further tools just isn’t essentially wanted.

Right here’re some breakdowns of a picture that was created in 2016 with the 50L utilizing this method:

The picture “The Galaxy Volcanic” above was created with 14 pictures complete with a Canon 50mm f/1.2L lens. The picture total would have benefited from an extra row on the prime to crop out all of the astigmatism inherent within the lens alternative. You reside and also you study. 

Under are the cropped pictures of the underside row of the panorama, staying across the Omega Nebula, close to the middle core of the Milky Manner, as the photographs had been taken left to proper. These are 1:1 cropped into the highest of the photographs. You may discover close to the highest of the picture, the celebs change sizes resulting from being close to corners of the picture.

This second set of pictures is the second row above the primary set of pictures, however the core on this case is extra central within the body, the place the perfect a part of the lens is situated. These pictures are 1:1 cropped into the middle of the body of every picture and present how little coma or astigmatism is within the middle. The photographs had been taken proper to left, however cropped to remain across the Omega Nebula close to the middle core of the Milky Manner.

If you happen to discovered this tip useful, let me know within the feedback. If you happen to’ve already been utilizing this method whether or not to get rid of astigmatism and coma or not, let’s see a number of the pictures you’ve created at night time.


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